Radio frequency control system



Nov. 21, 1950 c. s. MATLAND ETAL 2,530,979

RADIO FREQUENCY CONTROL SYSTEM Filed Sept. 2'7, 1945 Ante/Md 5. 12/ L7 43 L W l I 'j/l/f 7 A 10 Trams/miter t a /9 Face/Var WITNESSES: 6 6 /nv zmgas d ar a an an 7% M 8077 ffazz.

Patented Nov. 21, 1950 UNITED STATES PATENT OFFICE.

RADIO FREQUENCY CONTROL SYSTEM Carl G. Matland, New York, N. Y., and Leon Kata, Forest Hills, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application September 27, 1945, Serial No. 618,968

19 Claims. 1 This invention relates to a transmission system for electromagnetic waves and has particular relation to a system for use in radar equipment.

In the usual single antenna radar equipment, a transmitter is employed to develop high power signals in the form of pulses of ultra-high frequency electromagnetic energy. These pulses are conducted from the transmitter to the antenna through a suitable transmission line, such as a hollow wave guide. From the antenna the signals are propagated in a known direction. Upon striking an object the signals are reflected and the reflected signals are picked up by the antenna. The reflected signals, of course, are of a comparatively low power.

A receiving system for the reflected low power signals is also connected to the antenna by a coupling to the guide between the transmitter and the antenna. The receiving system comprises a local oscillator, a crystal mixer for receiving and mixing the reflected signals with the output of the local oscillator, and a receiver circuit including suitable amplifiers and indicators to which the output of the mixer is applied.

Since the high power signals introduced by the transmitter into the guide between the transmitter and antenna would be highly detrimental to the receiving system, a transmitter-receiver switch is interposed between the main guide and the receiving system. The purpose of the transmitter-receiver switch is to permit the low power reflected signals to pass to the receiver, but to prevent the high power signals from the transmitter from passing therethrough in suiflcient strength to damage the receiver. The usual transmitter-receiver switch comprises a cavity resonator having a low pressure electrode gap therein. The cavity resonator is tuned to the frequency of the electromagnetic waves of the radar signals. When the low power reflected signals are supplied to the resonator of the trans-.

mitter-receiver switch, it functions as an effective highly resonant circuit having a high Q, that is, a high ratio of the energy stored to the energy lost per cycle, and permits the transmission of the reflected signals therethrough to the receiving system. 4

On the other hand, high power signals from the transmitter cause an electric discharge to be established across the electrode gap in the res onator of the transmitter-receiver switch which changes the resonator from an effective resonant circuit to a nonresonant one having an extremely low Q. Consequently, the transmitter-receiver switch reflects most of the electromagnetic waves of the signal from the transmitter and prevents passage thereof to the receiving system.

It has been found desirable in many cases to provide a beacon system in corri'unction with the usualradar equipment especially where the radar equipment is mounted on a mobile unit, such as a ship or, an airplane. Such a combined arrangement performs the usual functions of radar equipment and, in addition, gives homing or position information to its operator. In atypical arrangement, several fixed ultra-high frequency transmitters, called beacon transmitters, are'located at known points. These beacon transmitters are capable of transmitting a coded set of signals which will convey to the operator information respecting his position. Operation of a beacon transmitter may be initiated b the receipt at the beacon station of a series of coded signals transmitted from the radar equipment.

The beacon signals are transmitted at a different electromagnetic wave frequency than the radar signals to avoid any conflict in the receiver between the two signals. The difference in electromagnetic wave frequency of the beacon and radar signals is sometimes as much as megacycles. Since the same antenna, transmitter-receiver switch and receiving system are used for the reception of both the reflected radar signals, and the beacon signals, it is apparent that unless the radar apparatus has a very broad frequency band, the beacon signal will not be received with the same sensitivity as the radar signal. But the transmitter-receiver switch is very frequency sensitive since it has a very high Q with respect to the transmission therethrough of the radar frequency signals. It follows that the transmitter-receiver switch is considerably of! resonance with respect to the beacon frequency signals. In typical beacon radar apparatus, the insertion loss for the beacon signal is as high as 15 to 18 decibels as compared with a loss of one decibel for the radar signal. Such a great loss of beacon signal power definitely limits the reliability and range of the present beacon systems.

It has also been found that the crystal of the receiving system of radar equipment, and partic- 3 Iide free electrons to aid in establishing the discharge across the electrode gap upon receipt of a high power signal. But when the equipment is shut down, the direct current are is discontinued so that the high power signals might not establish an arc in the electrode gap so that the full power is applied to the crystal. It is obviously highly desirable to avoid any such occurrence with the resulting damage to the crystal.

It is, accordingly an object of our invention to provide new and improved apparatus for use with a transmission system for electromagnetic waves for quickly and easily changing the characteristics thereof with respect to ability to conduct electromagnetic waves.

It is a further object of our invention to provide novel apparatus for use in radar equipment whereby both radar and beacon signals may be conducted to the receiving system without substantial attenuation of either.

Another object of our invention is to provide new and improved apparatus for use in radar equipment whereby the crystal of the receiving system is fully protected when the equipment is shut down.

A further object of our invention is to provide new and improved apparatus including a transmitter-receiver switch for use in radar equipment whereby both radar and beacon signals of different frequencies may be transmitted through the switch without substantial attenuation of either.

- More specifically, it is anobject of our inven- I tion to provide novel apparatus including a transmitter-receiver switch for use in radar equipment-whereby both radar and beacon signals may be transmitted to the receiving system without substantial attenuation of either and with full protection to the crystal when the equipment is shut down.

In accordance with our invention, we provide apparatus which is operable to cause the characteristics of the system including the cavity resonator of the transmitter-receiver switch to be changed either to retune the system from the radar frequency to the beacon frequency or substantially to prevent passage of waves through nected to the antenna I by means of an auxiliary hollow wave guide ll coupled to the main guide, and a crystal l3 inserted in the auxiliary guide near the end opposite the main guide and supported by a mounting IS on the outside thereof. The auxiliary guide II is divided into two sections and a transmitter-receiver switch I1 is interposed between the sections. A local oscillator IQ for use with radar signals is coupled to the system between the transmitter-receiver switch l1 and crystal l3. Another local oscillator 2| for use with beacon signals is also coupled to the system between the transmitter-receiver switch I! and the crystal I3.

As shown in Fig. 2, the section of the auxiliary guide ll, one end of which is coupled to the the system. The change is accomplished by inexpensive apparatus of rugged construction and may be made quickly and easily from a remote point. The retuning to the beacon frequency is arranged to permit passage through the transmitter-receiver switch of the beacon signals without substantial attenuation. On the other hand, changing the characteristics of the system to an even greater extent as to prevent substantially the passage of waves therethrough is useful in protecting the crystal of the receiving system when the equipment is shut down.

The features of our invention which we consider novel are set forth with more particularity in the appended claims. The invention itself, however, together with additional objects and advantages thereof, may be best understood from the following description of a specific embodiment when read in connection with the accompanying drawing, .in which:

Figure 1 is a schematic diagram of radar equipment embodying our invention; and

Fig. 2 is an enlarged cross-sectional view of the apparatus taken along line 11-11 of Fig. 1.

As shown in Fig. 1, a transmitter 3 is arranged to provide radar frequency signals to the antenna 5 through a suitable main transmission line, such "a's'a hollow wave guide I. A receiver 9 is conmain guide I, is connected at its other end to the body 23 of the transmitter-receiver switch I! by means of a flange 25 which forms a quarterwave length choke at the coupling joint and is bolted to the body 23. The guide II is formed of highly conductive material and is preferably in the shape of a rectangular pipe.

The transmitter-receiver switch I! and the arrangement for coupling it to a wave guide is shown and described in more detail in the copendlng application of D. Alpert, Serial No. 480,991, filed March 29, 1943, for an improvement in Ultra-High Frequency Tubes, which issued as Patent No. 2,525,468 on October 10, 1950, and assigned to the assignee of the present application. The switch ll comprises a hollow body 23 of highly conductive material arranged to form a cavity resonator having a chamber 26. A pair of vacuum-tight glass windows 21 at either side of the body 23 in line with the auxiliary wave guide ll form an inlet and an outlet for electromagnetic waves passing through the resonator. The interior of the body 23 is evacuated and a pair of electrodes 29 are positioned to form a low pressure electrode gap across the center of the resonator chamber 26. An auxiliary electrode 3| is provided in a small chamber 33 just outside the resonator chamber 26. This auxiliary electrode 3| may be connected through a suitably operated switch 35 to one terminal of a source of direct current voltage, illustrated as a battery 31, the other terminal of which is connected to the body 23 of the transmitterreceiver switch l1. When the switch 35 is closed, a small direct current are is established between the auxiliary electrode 3| and the body 23 to provide free electrons which may escape through a small opening 39 to the interior of the resonator chamber 26 to facilitate the establishment of an are between the main electrodes 29.

The resonator is tuned by an adjustable member II to the frequency of the transmitter 3. When high power signals of the radar frequency are supplied to the resonator of the transmitterreceiver switch ll, an arc is established between ceiver switch II at the outlet side thereof by means of the usual flange 43 with a quarterwave choke. The other end of this guide section is closed and the crystal ll of a suitable form is mounted across the guide II at substantially the center of the wider dimension thereof. The position of the crystal l3 and the closed end of the auxiliary guide section are such as to provide a matched load at the output of the transmitterreceiver switch 11.

The output of the beacon local oscillator 2| and that of the radar local oscillator I! are supplied to the auxiliary guide l'l between the trans- 4 mitter-receiver switch I1 and the crystal I! through appropriate openings in the narrower walls of the guide. One of these openings 48 is shown in Fig. 2 and the other is directly opposite and of the same configuration. Of course, only one local oscillator is operated at a time, depending upon whether radar or beacon signals are to be received. Suitable tuning screws 41 are provided at the point of coupling of the local oscillators to the auxiliary guide.

To effect retuning of the transmitter-receiver switch resonator, a first solenoid 49 is mounted on the guide ll adjacent the resonator and between the resonator and the local oscillation coupling points. The solenoid 4! comprises a conductive member, such as rod or plunger 5|, mounted at substantially right angles to the auxiliary guide H and in line with an opening 53 in one of the wider walls of the auxiliary guide. The plunger 5| is normally maintained outside the guide H in the position illustrated, by a spring 55. However, upon energization of the coil 51 of the solenoid 49 by closing a switch 5! completng a series circuit from a direct current voltage source, such as a battery ll through the coil 51, the plunger ii is pulled downward and moved into the guide II. The amount of movement of the plunger 5| into the guide ll may be adjusted by varying the threaded connection between the plunger SI and a stop member CI.

The size of the plunger SI and the extent of movement thereof into the guide l.l are chosen with respect to the location of the plunger relative to theresonator of the transmitter-receiver switch I'I so that when the plunger ii is moved into the guide II, the additional reactance afforded thereby causes the system to be retuned from the radar frequency to the beacon frequency. When the switch 59 in the solenoid coil circuit is opened, the spring 55 forces the plunger 5! back out of the guide II and the resonator is again tuned to the radar frequency.

In a specific application of the first solenoid and plunger in a 3.2 centimeter wave length radar system, it was found experimentally that optimum conditions were obtained with a inch plunger at the center of the wide dimension of the guide (i. e. conditions in which the shortest movement of the plunger was necessary and lowest loss was obtained for a given amount of retuning), when the distance from the adjacent surface of the transmitter-receiver switch was .880 inch. With this arrangement, the maximum loss on retuning to a frequency point 130 me. less than the original frequency point is 4 db. With the same apparatus a loss of 8 db is incurred without retuning of the system. The extent of movement of the plunger depends upon the amount of retuning desired.

To avoid undue leakage of power through the opening 53 in the guide II, the mounting 65 for the solenoid 49 is arranged to form a quarterwave choke at the opening it. Of course, if the opening II is provided in the center of a wider wall of a rectangular guide and is not too large, the leakage'of power might be suificiently small that the choke at the opening it could be eliminated.

A second solenoid i1 is mounted on the auiliary guide ll adjacent the resonator of the transmitter-receiver switch II. This second solenoid i1 is mounted on the wider wall of the guide ll opposite that on which the first solenoid 4! is mounted and also includes a movable rod or plunger I mounted at substantially right angles to the auxiliary guide ii in line with a second opening ll therein. The mounting ll for the second plunger II is also arranged to form a quarter-wave length choke at the opening II to prevent passage of electromagnetic energy therethrough. The second plunger I! is normally held outside the guide II by energisation of the coil ll of the solenoid 01 from the direct current source ll through another switch ll. When switch II is opened, a spring 11 forces the second plunger 8! into the uide ll. Movement of the second plunger ll into the guide is adjusted by the threaded connection at II to establish a short circuit across the guide and to reduce, efiectively, the size of the passageway through the guide to a point below the cut oil dimension whereby passage of electromagnetic waves therethrough is substantially prevented over a very wide frequency range. To establish the short circuit the second plunger is is caused to move substantially acrm and into contact with the opposite wall of the guide. If it does not actually engage the opposite wall, it is sufficiently close thereto and has sumcient area at its end to establish a large capacitance which is of low impedance to the high frequency currents and an effective short circuit. The diameter of the plunger is also of such size that the dimensions of the guide are reduced below the cut ofl point. Consequently, when the apparatus is shut down and the switch I! for the auxiliary electrode 3| of the transmitter receiver switch is opened as are the switches 59 and I! for the solenoids 49 and 61 the plunger 6! will be positioned within the guide II and will prevent passage of signals through the resonator of sufiicient strength to damage the crystal l3.

The second plunger is, of course, effective if used any place in a hollow guide to cause very substantial attenuation. However, the eifect for any given size of plunger causing less than complete cut oil is increased if the plunger is positioned a distance of the order of one-half wave length in the guide behind the resonator of the transmitter-receiver switch. Then the shortcircuiting eflect of the plunger acts to enforce the low impedance effect at the resonator for waves of other than the resonant frequency.

To avoid conflict between the plungers SI and 60 of the .two solenoids l9 and 61, the switches II and I6 controlling the solenoids may have an interiock '3 provided therebetween whereby the first solenoidcoil 51 cannot be energized to move the plunger 5| thereof into the guide H unless the second solenoid coil 13 is energized to move its plunger N out of the guide II.

It is to be understood that while we have shown the plungers ii and it operated by solenoids, they may, if desired, be operated by other means or even manually. In actual practice the apparatus is ordinarily inaccessible to the operator so that solenoid operation is particularly op-2a advantageous. Moreover, while'we'have shown the plungers-used with rectangular guides, they embodiment oLour. invention, we do not wish to restrict our inventionethereto; as we are aware that many modifications thereof may be made withoutndeparting .fromthe spirit of the invention. 1

We claim as our invention:

1. In a transmission system for electromagnetic waves. a wave guide having an openingin a wall thereof, and a conductive plunger movably mounted outside said guide at said opening and a solenoid operable to effect movement of said plunger into and out of said guide through said opening to change discretely the characteristics of said system with respect to the conduction of waves therethrough.

2. In a transmission system for electromagnetic waves, a wave guide having an opening in a wall thereof, a conductive plunger and means for mounting said plunger for movement through said opening, said mounting means including means cooperating with said plunger to form a choke substantially preventing energy loss through said opening, and a solenoid connected to said plunger and operable to move said plunger into and out of said guide through said opening to cause discrete changes in the characteristics of said system with respect to the conduction of waves therethrough.

3. In a. transmission system for electromagnetic waves, a wave guide having an opening in a wall thereof, a conductive plunger slidably mounted substantially perpendicular to said guide at said opening and a solenoid adapted to move said plunger into and out of said guide through said opening to cause discrete changes in the characteristics of said system with respect to the conduction of waves therethrough.

4. In a transmission system for electromagnetic waves, a wave guide having an opening in a wall thereof, and a solenoid including a conductive plunger movably mounted on said guide at said opening, said solenoid being operable to eflect movement of said plunger into and out of said guide through said opening to cause discrete changes in the characteristics of said system with respect to the conduction of waves therethrough.

5. In a, transmission system for electromagnetic waves, a cavity resonator into which electromagnetic waves are to be introduced, a wave guide coupled to said resonator to conduct electromagnetic waves from said resonator, said system including said resonator being tuned to a first predetermined frequency whereby waves of said first frequency may be conducted therethrough without substantial attenuation, said guide having an opening therein adjacent said resonator, and a conductive plunger movably mounted at said opening and a solenoid adapted to move abruptly said plunger into said guide through said opening to introduce a reactance in said system effective to retune said system including said resonator to a second predetermined frequency whereby waves of said second frequency may be conducted therethrough without substantial attenuation. Y

6. In a transmission system for electromagnetic waves, a cavity resonator into which electromagnetic waves are to be introduced, a wave guide coupled to said resonator to conduct electromagnetic waves from said resonator, said system including said resonator being tuned to a first predetermined frequency whereby waves of said first frequency may be conducted therethrough without substantial attenuation, said guide having an opening therein adiacent said resonator, and a conductive plunger movably mounted substantially perpendicular to said guide at said opening and a solenoid adapted to abruptly move said plunger a preselected distance into said guide through said opening to introduce a reactance in said system eflective to retune said system including said resonator to a second predetermined frequency whereby waves of said second frequency may be conducted therethrough without substantial attenuation.

7. In a transmission system for electromagnetic waves,.a cavity resonator into which electromagnetic waves are to be introduced, a wave guide coupled to said resonator to conduct electromagnetic waves from said resonator, said sys tem including said resonator being tuned to a first predetermined frequency whereby waves of said first frequency may be conducted therethrough without substantial attenuation, said guide having an opening therein adjacent said resonator, a conductive plunger, and means including a solenoid for slidably mounting said plunger at said opening, said plunger being adapted to be abruptly slid a preselected distance into said guide through said opening to introduce a reactance in said system elfective to retune said system including said resonator to a second predetermined frequency whereby waves of said second frequency may be conducted therethrough without substantial attenuation, said mounting means including means cooperating with said plunger to form a choke substantially preventing energy loss through said opening.

8. In a transmission system for electromagnetic waves, a cavity resonator into which electromagnetic waves are to be introduced, a wave guide coupled to said resonator to conduct electromagnetic waves from said resonator, said system including said resonator being tuned to a first predetermined frequency whereby waves of said first frequency may be conducted therethrough without substantial attenuation, said guide having an opening therein adjacent said resonator, and a solenoid including a conductive plunger slidably mounted at said opening, said solenoid being operable to effect movement of said plunger a preselected distance into said guide through said opening to introduce a reactance in said system effective to retune said system including said resonator to a second predetermined frequency whereby waves of said second frequency may be conducted therethrough without substantial attenuation.

9. In a transmission system for electromagnetic waves within a predetermined band of frequencies, a wave guide having an opening in a wall thereof, a conductive plunger, and means including a solenoid for effecting discrete movement of said plunger into said guide through said opening, said mounting including means cooperating with said plunger to form a choke substantially preventing loss of electromagnetic energy through said opening to reduce the effective size of said guide below that necessary to permit a substantially unattenuated conduction therethrough of waves within said band.

10. In a transmission system for electromagnetic waves within a predetermined band of frequencies, a wave guide having an opening in a wall thereof, and a solenoid including a conductive plunger slidably mounted substantially perp'endicular to said guide at said opening, said solenoid being operable to slide said plunger into and out of said guide through said opening with said plunger being of a size effective when moved into said guide to reduce the effective cross-sectional area of said guide below that necessary to permit a substantially unattenuated conduction therethrough of waves within said band.

11. In a transmission system for electromagnetic waves within a predetermined band of frequencies, a cavity resonator into which electromagnetic waves are to be introduced, a wave guide coupled to said resonator to conduct electromagnetic waves from said resonator, said guide having an opening therein a distance from the resonator of the order of an even number of half wave lengths in the guide, and a conductive plunger movably mounted substantially perpendicular to said guide at said opening and adapted to be moved into said guide through said opening to establish in effect a short circuit across said guide with said plunger being of a size effective when moved into said guide to reduce the effective cross-sectional area of said guide below that necessary to permit a substantially unattenuated conduction therethrough of waves within said band.

12. For use with a radar-beacon system including a transmitter; an antenna into which said transmitter operates; a receiver capable of receiving the radar frequency; and the beacon frequency; the combination comprising a wave guide section for interconnecting said antenna and said receiver and an electrical .switching mechanism including a solenoid controlled conductive plunger adapted for discrete movement into and out of said wave guide for rendering said wave guide selectively conductive to said radar or beacon frequencies.

13. For use with a communication system including an antenna, a receiver capable of receiving a first frequency and a second frequency; the combination comprising a common conductor comprising a wave guide for interconnecting said antenna and said receiver and an electrical switching mechanism including a solenoid operated conductive plunger adapted for discrete movement into and out of said wave guide for rendering said conductor selectively conductive to said first or said second frequencies.

'14. For use with a communication system including an antenna; the combination comprising a receiver having a converter, 9. first local oscillator cooperative with said receiver to render it capable of receiving a first frequency, .a second local oscillator cooperative with said receiver to render it capable of receiving a second frequency, a common conductor comprising a wave guide interconnecting said local oscillators and said converter with said antenna and an electrical switching mechanism including a solenoid operated conductive plunger adapted for discrete movement into and out of said wave guide for rendering said conductor selectively conductive to said first frequency or to said second frequency.

15. For use with a communication system including an antenna and a receiver; the combination comprising a conductor comprising a wave guide for interconnecting said receiver and said antenna and an electrical switching mechanism including a solenoid operated conductive plunger adapted for discrete movement into said wave 75 guide for rendering said conductor non-conductive to the radiation received by said antenna.

16. For use with a communication system including an antenna and a receiver having a supply of power and a converter of the crystal type; the combination comprising a conductor comprising a wave guide for interconnecting said receiver and said antenna and an electrical switching mechanism including a solenoid operated conductive plunger adapted for discrete movement into said wave guide to be actuated when said receiver is deprived of power for rendering said conductor non-conductive to the radiation received by said antenna.

1'7. A communication system including an antenna, a receiver having a converter of the type damaged when excessive energy is impressed thereon, terminals to be energized to supply power to said converter, a device for protecting said converter from excessive energy, said device being capable of protecting said converter when said terminals are energized and incapable when said terminals are deenergized, a conductor comprising a wave guide connecting said receiver to said antenna through said protective device and an electrical switching mechanism, said switching mechanism including a solenoid actuated conductive plunger adapted for discrete movement into said wave guide, to be actuated when said terminals are deenergized, for rendering said conductor non-conductive to energy received by said antenna.

18. A communication system including an antenna, a receiver having a converter of the type damaged when excessive energy is impressed thereon, a device for protecting said converter from excessive energy, terminals to be energized to render said protective device capable of protecting said converter, a conductor including a wave guide connecting said receiver to said antenna through said protective device and an electrical switching mechanism, said switching mechanism including a solenoid operated conductive plunger adapted for abrupt movement into said wave guide, to be actuated when said terminals are deenergized, for rendering said conductor non-conductive to energy received by said antenna.

19. A communication system including an antenna, a receiver having a converter of the type damaged when excessive energy is impressed thereon, a device for protecting said converter from excessive energy, terminals to be energized to render said protective device capable of protecting said converter, a wave guide connecting said receiver to said antenna through said protective device and an electrical switching mechanism, including a solenoid controlled conductive plunger-adapted for discrete movement into said wave guide, to be actuated when said terminals are deenergized, for rendering said wave guide non-conductive to energy received by said antenna.

CARL G. MATLAND. LEON KATZ.

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UNITED STATES PATENTS Number Name Date 2,158,584 Koster May 16, 1939 2,374,810 Fremlin May 1, 1945 (Other references on lollowinl Pile) 11. UNITED STATES PATENTS Number 2,373.233 2,401,425 2,401,489

ammo

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